I also suggest going BB
However, if you are intent on re-using your sandbed, here is what I have done when moving tanks and sandbeds:
- make sure you have lots of NSW made up to replace water you will lose during the move. Scrubbing off hair algae and a good swishing in lower salinity water (say, 1.016 to 1.020) will remove detritus that has gathered in the crevices of your rock without harming your bacteria. Don't know how much LR you have, but be prepared for the scrubbing and swishing process to dirty your water quickly. When the water gets too dirty, dump it and start with more clean water.
- once you get the livestock out of the display tank and put in your temporary tank, there should be 2"-3" of water left with the sandbed. Get a large rigid plastic spoon and stir up the sandbed. This will off-gas the anaerobic gases as well as loosen the detritus, leaving you with stinky filthy water. Move the sandbed to one side so you can siphon out the dirty water. To clean the further the sandbed, add more SW and stir it up again. And, again, your water will be pretty dirty. Push the sand to the side and siphon again. Once you see how dirty your sandbed is, even after several cleanings, you may wish to go BB. IME, adding a new sandbed will only give you another dirty sandbed in a few months or years.
- the walls of your tank may be covered in algae and coralline. During the time you've had most of the water out of the tank, this once live stuff will have died. You will need to remove the sandbed, then scrape off the dead algae and coralline. Rinse with tapwater, siphon as much dead stuff out, then towel out the last of the dead stuff.
- replace the sandbed, if you are so inclined, put in enough water so you can keep it heated and aerated while you are deciding when to put back your rock and livestock. I have done this whole process in a day when moving to another house, so I don't see a problem with putting your livestock back into the tank once you've cleaned the tank and sandbed.